Greater Hartford is the second-richest urban area in the country, after the Silicon Valley, and is fourth-richest in the world, according to the latest Metro Monitor study from the Brookings Institution.

Wait, what? Hartford is richer than Fairfield County? How can that be?

It depends on what you measure. Hartford's residents do not earn more than Fairfield County residents. In metro Hartford, the average earnings were $89,700 in 2013, according to the U.S. Census. In Fairfield County, average earnings were $136,019 — 50 percent more.

Instead, Hartford's high ranking is based on a combination of income paid to local residents — still very high, in the big picture — and corporate profits that were not distributed as dividends from local companies.

Greater Hartford had $76,510 in GDP for each resident of the three-county metro area, and Fairfield County had $68,570.

Zurich is at the top of the list, and Oslo is second. Fairfield County is No. 8 worldwide, just behind Boston.

"There's an incredible concentration of advanced services that create a ton of output," said Joseph Parilla, lead author of the report, released Thursday. And, when those advanced services cost a lot but don't require that many local people to produce them, the figure looks even better.

That's the flip side of the study. While Hartford is near the top in relative wealth, it's near the bottom in growth. That's true generally in the world. Cities like Calcutta and Bangalore, India, which were at the very bottom in GDP per capita in the list of the 300 largest urban areas in the world, are also growing faster.

Calcutta was 32nd in economic growth — and nearly all of the top 10 percent of the growth list were Third World countries, with the notable exception of Dubai.

Greater Hartford was 239, just behind Detroit and Buffalo, when the speed of growth of output and jobs was compared from 2013 to 2014.

Parilla said while the GDP per capita figure doesn't tell you anything about the distribution of income — median income is a better measure of how well off the average person is — it was the only figure available for all the cities around the world.

Robert Frank, an economics professor at Cornell University, who has written about the inadequacy of per capita GDP as a measure of well-being, said that nationwide, GDP growth has been a straight diagonal line up, while incomes have stagnated for most people below the very top.

He said the fact that Hartford had a higher GDP per person than Fairfield County is an anomaly, given that Fairfield County has higher income (including investment and retirement income) and earnings.